Do not treat callbacks with no handlers as interfaces.

lib/dom/scripts/dartgenerator.py

Index: lib/dom/scripts/dartgenerator.py
diff --git a/lib/dom/scripts/dartgenerator.py b/lib/dom/scripts/dartgenerator.py
index c5c4be55c09e730ddbdb066b82fea7b257559e7f..9d2fa53b299bc2585f74ebe2daac3a20eb359c5d 100755
--- a/lib/dom/scripts/dartgenerator.py
+++ b/lib/dom/scripts/dartgenerator.py
@@ -223,12 +223,15 @@ class DartGenerator(object):
             interface_name, auxiliary_file))
         continue
 
-      info = RecognizeCallback(interface)
-      if info:
-       system.ProcessCallback(interface, info)
-      else:
-        if 'Callback' in interface.ext_attrs:
+      if 'Callback' in interface.ext_attrs:
+        handlers = [op for op in interface.operations if op.id == 'handleEvent']
+        if not handlers:
+          # FIXME: fix MutationCallback and assert(handlers).
           _logger.info('Malformed callback: %s' % interface.id)
+          continue
+        info = AnalyzeOperation(interface, handlers)
+        system.ProcessCallback(interface, info)
+      else:
         _logger.info('Generating %s' % interface.id)
         system.ProcessInterface(interface)